The present invention relates to the procedures for manufacturing metal articles of intricate profile by permanent connection of their components which may be effected by various methods, such as: welding, shrink-fit, etc., and to moulds for casting at least one of the components of such articles.
The present invention can find application in the production of, e.g., fitting valve bodies for power plants of steam power stations, crankshafts and connecting rods for high-duty diesel engines, propellers, pressure vessels with pipe-branches, heavy pieces of variable cross section, made conventionally from forged blanks, etc.
Known in the art is a method for manufacturing complex-shaped articles by welding together separate components. For example, vessel casings may be made from individual prefabricated parts encluding shells, bottoms and connecting pieces; gas or steam turbine rotors may be made from separate shafts, disks, rings, etc.
Also known is a procedure for the fabrication of heavy size crankshafts by joining together crankwebs and pins, which have been produced separately. Steel crankwebs are sand-cast, while crankpins are manufactured by forging ingots. After appropriate mechanical working, the webs are fitted with holes and the crankpins turned, whereupon they are shrink-fitted to obtain a crankshaft. The above technique is being used by the Danish company, Burmeister and Wain in producing crankshafts for ship diesel engines.
Well known are moulds for casting various articles or their components by electroslag remelting of, say, a consumable electrode (see, for example, G. Bhat, "Current Progress with Electroslag Remelting -Scientific Problems of Welding and Special Electrical Metallurgy, Pt 4" Naukova Dumka, Kiev, 1970).
However, the known process is disadvantageous in that the production of welded construction in general, and vessel casings, gas and steam turbine rotors, etc., in particular, is a very labor-consuming operation and, first and foremost, an operation which involves a large volume of erection welding. The process of welding wide pre-fabricated parts of, e.g., alloyed steels, becomes a problem, since it requires preheating prior to welding. At the present time some high-tensile steel grades do not lend themselves to welding at all.
The known method of manufacturing crankshafts by joining together the crankwebs and pins with the use of a shrink-fit is not free of serious shortcomings and disadvantages either.
Firstly, in sand-casting of crankwebs a large percentage of rejects may occur. In the second place, as-cast metal features rather inferior mechanical properties, especially in terms of its ductility. Thirdly, inherent in the foregoing technique, according to which crankwebs and pins are shrink-fitted to join them together, is a very low metal use factor. This is attributed to the fact that with a single view to providing a reliable connection between the crankweb and the crankpin, it is necessary to have around the fit holes in the crankweb a considerable amount of metal, which actually does not take part in the web operation.
Attempts to produce crankshafts by coupling separate pre-cast or pre-forged cranks have also proved rather inadequate, since in either case they call for a substantial increase in both labor requirements and the initial cost of the crankshafts.